A time to digital converter (TDC) is typically used to digitize a time delay value between two different signals. A TDC determines the delay, for example, between a signal edge in a reference signal and a signal edge in an input signal to the TDC. Typically, a TDC will output a digital code value which represents this time delay value between the signals.
A TDC is commonly used in a digital phase-locked loop (PLL). PLLs are used, for example, to lock the phase difference between the two different signals, and this locking will result in the input and output frequencies of a PLL to be the same or synchronized. PLLs can also generate a frequency that is a multiple of the input frequency. PLLs are widely used in, for example, radio, telecommunications, computers, and other applications.